These studies of myeloid leukemia in RFM mice will provide further insight into factors which influence the rate of growth of myeloid leukemia cells, the differentiation potential of myeloid leukemia stem cells and the usefulness of the RFM murine myeloid leukemia as an animal model of human myeloid leukemia. Studies will include: (a) Study of the numbers of hemopoietic stem cells in marrow, spleen, liver and blood during early, mid and late stages of the disease, (b) study of the effect of the amount of normal hemopoietic tissue on the growth rate of transplanted leukemic stem cells, (c) study and comparison of the characteristics of leukemic and normal CFU-C, (d) study of the role of the spleen on the development of transplanted myeloid leukemia, (e) study of the effect of humoral substances in leukemic RFM mice on the growth of normal marrow cells in intra-peritoneal diffusion chambers, (f) study of genetic markers of tissues and cells of leukemic mice, (g) study of the cytogenetics of this murine myeloid leukemia, (h) study of the effect of chemotherapeutic agents on the growth of myeloid leukemia in RFM mice.